Parboil cabbage long enough so that the leaves separate without tearing.
Select 10 or 12 of the largest leaves; trim off the midribs so leaves become easy to roll.
Reserve remaining cabbage for other use.
Soak bread in water and squeeze out; or moisten bread crumbs.
Combine with meat and mix thoroughly.
Add onion, egg, and seasoning and mix again.
Divide into as many portions as there are cabbage leaves.
Spread mixture evenly on leaves.
Roll firmly, tucking edges inside so that stuffing will not escape, and secure with cotton string.
If there are not enough large leaves, use 2 small leaves, letting them overlap.
Arrange cabbage birds tightly in a saucepan, add a small quantity of bouillon, and simmer over low heat until tender.
Remove string.
For the sauce, make a roux with flour and butter, add tomato paste and bouillon from stuffed cabbage; stir until smooth and bubbly.
Season to taste and let the sauce simmer for a few more minutes.
Arrange cabbage on a hot platter, pour sauce over it, and serve with potatoes.